From e4137f08816bbf91fe76d1b60fa16862a4827ac1 Mon Sep 17 00:00:00 2001
From: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
Date: Fri, 11 Oct 2024 08:53:10 +0500
Subject: [PATCH] mm, kasan, kmsan: instrument copy_from/to_kernel_nofault
Instrument copy_from_kernel_nofault() with KMSAN for uninitialized kernel
memory check and copy_to_kernel_nofault() with KASAN, KCSAN to detect the
memory corruption.
syzbot reported that bpf_probe_read_kernel() kernel helper triggered KASAN
report via kasan_check_range() which is not the expected behaviour as
copy_from_kernel_nofault() is meant to be a non-faulting helper.
Solution is, suggested by Marco Elver, to replace KASAN, KCSAN check in
copy_from_kernel_nofault() with KMSAN detection of copying uninitilaized
kernel memory. In copy_to_kernel_nofault() we can retain
instrument_write() explicitly for the memory corruption instrumentation.
copy_to_kernel_nofault() is tested on x86_64 and arm64 with
CONFIG_KASAN_SW_TAGS. On arm64 with CONFIG_KASAN_HW_TAGS, kunit test
currently fails. Need more clarification on it.
[akpm@linux-foundation.org: fix comment layout, per checkpatch
Link: https://lore.kernel.org/linux-mm/CANpmjNMAVFzqnCZhEity9cjiqQ9CVN1X7qeeeAp_6yKjwKo8iw@mail.gmail.com/
Link: https://lkml.kernel.org/r/20241011035310.2982017-1-snovitoll@gmail.com
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
Reviewed-by: Marco Elver <elver@google.com>
Reported-by: syzbot+61123a5daeb9f7454599@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=61123a5daeb9f7454599
Reported-by: Andrey Konovalov <andreyknvl@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com> [KASAN]
Tested-by: Andrey Konovalov <andreyknvl@gmail.com> [KASAN]
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/kasan/kasan_test_c.c | 36 ++++++++++++++++++++++++++++++++++++
mm/kmsan/kmsan_test.c | 17 +++++++++++++++++
mm/maccess.c | 10 ++++++++--
3 files changed, 61 insertions(+), 2 deletions(-)
diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
index d8fb281e439d..fe132ce3c2b3 100644
--- a/mm/kasan/kasan_test_c.c
+++ b/mm/kasan/kasan_test_c.c
@@ -1928,6 +1928,41 @@ static void rust_uaf(struct kunit *test)
KUNIT_EXPECT_KASAN_FAIL(test, kasan_test_rust_uaf());
}
+static void copy_to_kernel_nofault_oob(struct kunit *test)
+{
+ char *ptr;
+ char buf[128];
+ size_t size = sizeof(buf);
+
+ /*
+ * This test currently fails with the HW_TAGS mode. The reason is
+ * unknown and needs to be investigated.
+ */
+ KASAN_TEST_NEEDS_CONFIG_OFF(test, CONFIG_KASAN_HW_TAGS);
+
+ ptr = kmalloc(size - KASAN_GRANULE_SIZE, GFP_KERNEL);
+ KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+ OPTIMIZER_HIDE_VAR(ptr);
+
+ /*
+ * We test copy_to_kernel_nofault() to detect corrupted memory that is
+ * being written into the kernel. In contrast,
+ * copy_from_kernel_nofault() is primarily used in kernel helper
+ * functions where the source address might be random or uninitialized.
+ * Applying KASAN instrumentation to copy_from_kernel_nofault() could
+ * lead to false positives. By focusing KASAN checks only on
+ * copy_to_kernel_nofault(), we ensure that only valid memory is
+ * written to the kernel, minimizing the risk of kernel corruption
+ * while avoiding false positives in the reverse case.
+ */
+ KUNIT_EXPECT_KASAN_FAIL(test,
+ copy_to_kernel_nofault(&buf[0], ptr, size));
+ KUNIT_EXPECT_KASAN_FAIL(test,
+ copy_to_kernel_nofault(ptr, &buf[0], size));
+
+ kfree(ptr);
+}
+
static struct kunit_case kasan_kunit_test_cases[] = {
KUNIT_CASE(kmalloc_oob_right),
KUNIT_CASE(kmalloc_oob_left),
@@ -2000,6 +2035,7 @@ static struct kunit_case kasan_kunit_test_cases[] = {
KUNIT_CASE(match_all_not_assigned),
KUNIT_CASE(match_all_ptr_tag),
KUNIT_CASE(match_all_mem_tag),
+ KUNIT_CASE(copy_to_kernel_nofault_oob),
KUNIT_CASE(rust_uaf),
{}
};
diff --git a/mm/kmsan/kmsan_test.c b/mm/kmsan/kmsan_test.c
index 13236d579eba..9733a22c46c1 100644
--- a/mm/kmsan/kmsan_test.c
+++ b/mm/kmsan/kmsan_test.c
@@ -640,6 +640,22 @@ static void test_unpoison_memory(struct kunit *test)
KUNIT_EXPECT_TRUE(test, report_matches(&expect));
}
+static void test_copy_from_kernel_nofault(struct kunit *test)
+{
+ long ret;
+ char buf[4], src[4];
+ size_t size = sizeof(buf);
+
+ EXPECTATION_UNINIT_VALUE_FN(expect, "copy_from_kernel_nofault");
+ kunit_info(
+ test,
+ "testing copy_from_kernel_nofault with uninitialized memory\n");
+
+ ret = copy_from_kernel_nofault((char *)&buf[0], (char *)&src[0], size);
+ USE(ret);
+ KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+}
+
static struct kunit_case kmsan_test_cases[] = {
KUNIT_CASE(test_uninit_kmalloc),
KUNIT_CASE(test_init_kmalloc),
@@ -664,6 +680,7 @@ static struct kunit_case kmsan_test_cases[] = {
KUNIT_CASE(test_long_origin_chain),
KUNIT_CASE(test_stackdepot_roundtrip),
KUNIT_CASE(test_unpoison_memory),
+ KUNIT_CASE(test_copy_from_kernel_nofault),
{},
};
diff --git a/mm/maccess.c b/mm/maccess.c
index 518a25667323..3ca55ec63a6a 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -13,9 +13,14 @@ bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
return true;
}
+/*
+ * The below only uses kmsan_check_memory() to ensure uninitialized kernel
+ * memory isn't leaked.
+ */
#define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \
while (len >= sizeof(type)) { \
- __get_kernel_nofault(dst, src, type, err_label); \
+ __get_kernel_nofault(dst, src, type, err_label); \
+ kmsan_check_memory(src, sizeof(type)); \
dst += sizeof(type); \
src += sizeof(type); \
len -= sizeof(type); \
@@ -49,7 +54,8 @@ EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
#define copy_to_kernel_nofault_loop(dst, src, len, type, err_label) \
while (len >= sizeof(type)) { \
- __put_kernel_nofault(dst, src, type, err_label); \
+ __put_kernel_nofault(dst, src, type, err_label); \
+ instrument_write(dst, sizeof(type)); \
dst += sizeof(type); \
src += sizeof(type); \
len -= sizeof(type); \